Clooney portrayed Dr. Doug Ross, the womanizing pediatrician with a heart of gold, on the hit series from its inception in 1994 to 1999. His role as Dr. Doug is widely considered to have been Clooney’s major break in show business, despite his previous recurring roles on The Facts of Life and Roseanne.

Clooney has of course moved on to become a suave cinematic icon in such films as Out of Sight, Ocean’s 11, The Perfect Storm, Good Night and Good Luck, and Michael Clayton.

A+E Interactive reports that Clooney’s willingness to return to the TV series that spawned him comes as a shock. Just a few days ago at a press conference, ER producer John Wells stated that he didn’t think Clooney would return.

Bosses on the longtime NBC series have labored to make this final season a memorable sendoff by recruiting guest appearances from actors who have since left the show.

Anthony Edwards (who played the now deceased Dr. Mark Greene until season 8) returned for a brief flashback this season.

More past stars are expected to return as well, including Juliana Marguiles, who played Nurse Carol Hathaway (Clooney’s onscreen love). Her last episode coincided with Clooney’s last appearance on the show—a surprise cameo in season 6.

Marguiles, according to ET, is also taping scenes this week to reprise her star turn.

Will her character and Clooney’s Dr. Doug still be together? You’ll just have to tune in.